1. Field of the Invention
The invention relates to a driving force control apparatus and a driving force control method. More particularly, the invention relates to a driving force control apparatus and a driving force control method which change a shift speed from an optimal shift speed for passing the starting point of a curve to an optimal shift speed for passing the end point of the curve at an optimal time point when the vehicle goes round the curve.
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-2000-27981 describes a shifting control apparatus which includes a starting-point control means, a curve control means, an end-point control means, and selection control means. The starting-point control means sets a driving force appropriate for passing the starting point of a curve ahead of a vehicle, based on an optimal driving force at each point of a road ahead of the vehicle. The optimal driving force at each point is calculated based on the road condition at each point. When the curve control means determines that the vehicle is going through the curve where the vehicle needs to turn by a predetermined amount or more, the curve control means sets a driving force appropriate for going through the curve. When the end-point control means determines that the vehicle is running toward the end point of the curve, the end-point control means sets a driving force appropriate for passing the end point of the curve. The selection control means selects the maximum driving force, among the driving forces set by the starting-point control means, the curve control means, and the end-point control means.
Japanese Patent Application Publication No. JP-A-2002-122225 describes a shifting control apparatus. The shifting control apparatus executes a cooperative shifting control for an automatic transmission, based on information relating to the condition around a vehicle or the condition ahead of the vehicle. In the shifting control apparatus, a cooperative shifting control means directly determines a shift speed that should be selected, based on the information regarding the actual curvature of a road (the curvature radius R of a road) and information on the gradient of a road surface (road surface gradient θR). The cooperative shifting control means changes the shift speed to the determined shift speed. As a result, the shift speed or the speed ratio appropriate for the curvature of the road or the gradient of the road surface is achieved promptly.
When a downshift control for a transmission is executed while a vehicle goes round a curve, an optimal shift speed (speed ratio) for passing the starting point of the curve may be different from an optimal shift speed (speed ratio) for passing the end point of the curve. In most cases, the optimal shift speed for passing the end point of the curve is higher than the optimal shift speed for passing the starting point of the curve. The optimal shift speed for passing the starting point of the curve is determined based on the deceleration required to pass the starting point of the curve. The optimal shift speed for passing the end point of the curve is determined based on the driving force required to pass the end point of the curve. As a result, both the shift speeds may be different from each other. However, in conventional technologies, for example, in the technology described in the aforementioned Publication No. JP-A-2002-122225, the same shift speed is selected at the starting point of the curve, and at the end point of the curve. That is, the optimal shift speed is not necessarily selected at the starting point of the curve, and at the end point of the curve.
After the downshift control is executed to pass the starting point of the curve, upshift control may be executed to pass the end point of the curve so that the optimal braking force and the optimal driving force are provided at the starting point of the curve and at the end point of the curve. However, there is no technology that determines the time point at which the shift speed should be changed.